1. Field of the Invention
This invention relates to the field of processes for treating spent alkaline reagents and, more particularly, to such processes in which the spent alkaline reagents are obtained from the treatment of hydrocarbon fluids such as are encountered in petroleum refining operations.
2. Description of the Prior Art
Hydrocarbon distillates such as gasoline, naphtha, jet fuel, kerosene, diesel fuel, or fuel oil containing mercaptans and hydrogen sulfide are commonly referred to as "sour" and are usually unsatisfactory for their intended uses. Mercaptans have a highly offensive odor even in minor concentrations. Their presence in gasoline impairs its susceptibility to octane-improvement through the addition of compounds such as tetraethyl lead. When mercaptans are pyrolyzed they yield undesirable atmospheric contaminants in the form of sulfur oxides.
In current refining practice, hydrogen sulfide is generally first removed from a sour distillate by contacting the distillate with a suitable selective solvent such as monoethanol amine. Thereafter, mercaptans are removed from the distillate by reaction with an alkaline reagent thus forming water-soluble alkali metal mercaptides (i.e., spent alkaline reagent).
Any suitable alkaline reagent may be employed including particularly sodium hydroxide (caustic), potassium hydroxide, etc. The alkaline reagent generally is utilized as an aqueous solution of from about 5% to about 50% weight concentration and, when desired, solutizers, solubilizing agents, etc., are employed including, for example, alcohols and particularly methanol, ethanol, etc., phenols, cresols, butyric acid, etc., in order to increase the contact and/or reaction of the acidic components with the alkaline reagent. A number of processes are known for regenerating the alkaline reagent, basically by oxidation of the mercaptide salts to organo-disulfides. In such processes, the aqueous mercaptide-containing phase is removed from the hydrocarbon phase and is contacted with an oxygen-containing gas, ozone, etc., at ambient or slightly elevated temperature to convert the alkali metal mercaptides to organo-disulfides and regenerate alkali metal hydroxide for reuse in sweetening. Variations of the foregoing caustic regeneration process are described in U.S. Pat. Nos. 2,001,715; 2,369,771; 2,425,414; 2,516,837; 2,525,583; 2,583,136; 2,599,449; 2,651,595; 2,719,109; 2,740,748; 2,747,969; 3,757,074; 2,760,909; 2,794,767; 2,853,432; 2,882,132; 2,844,440; 3,023,084; and, 4,090,954, among others.
The American Petroleum Institutes "Manual on Disposal of Refinery Wastes/Volume on Liquid Wastes" (1969) generally discloses that air oxidation of spent alkaline solutions can be used to reduce chemical oxygen demand (COD) prior to biological treatment. However, it has been observed experimentally that an oxidation by itself does not lead to a gross reduction in COD and must be accompanied by a further treatment to render the spent alkaline solutions suitable for discharge to waste.
While FMC Corporation has described in its brochure "Hydrogen Peroxide Waste Treatment by Industry" a variety of industrial effluent treatments employing hydrogen peroxide, the publication neither discloses nor suggests the treatment of spent alkaline reagent derived from petroleum processing operations employing hydrogen peroxide.